The present invention relates to a control of an automotive continuously variable transmission (CVT), and more particularly to a CVT ratio rate control.
Previously, there have been various methods to control the automotive CVT ratio. The most straight forward way is to define a desired CVT ratio in response to a vehicle speed and a power request command, such as a throttle opening degree or a depression of gas pedal, and then adjust an actuator, such as, a stepping motor, of a ratio control element of the CVT in a manner to achieve that CVT ratio. There occurs a change in desired CVT ratio toward the minimum or smallest ratio in response to a quick release of a gas pedal. Thus, the CVT ratio begins to change in upshift direction immediately after the operator has released the gas pedal quickly. This change in CVT ratio causes inertia of the engine, causing a peak in output torque of the CVT. Due to this torque peak, the operator experiences ride feel that the automotive vehicle is thrown forwardly or feels shocks. Besides, engine brake performance is not satisfactory.
What is desirable in driving an engine-CVT system is CVT ratio control dependent on the rate of change per unit time of the position of a gas pedal toward a released position thereof.